1. Field of the Invention
The invention relates to data processing systems and more particularly to apparatus for controlling message transfers within a local area network.
2. Description of the Related Art
A Local Area Network, or LAN, is a data communications system which allows a number of independent devices to communicate with each other within a moderately sized geographical area. The term LAN is used to describe networks in which most of the processing tasks are performed by a workstation such as a personal computer rather than by shared resources.
A LAN consists of a desktop workstation which performs processing tasks and serves as the user's interface to the network. A wiring system connects the workstations together, and a software operating system handles the execution of tasks on the network.
In the above-referenced application Ser. No. 07/291,700 there is described a Local Area Network architecture based on a active star topology. Nodes attach to the hub of the star through duplex communication links. Messages transferred between nodes are passed through the hub, which is responsible for arbitration and routing of messages. Unlike the prior bus topology, or ring topology, each node of the active star receives only those messages that are intended for it. Routing of messages is accomplished by a destination address in the header of the message. Destination addresses are unique to each node and provide the means by which the hub keeps the communication between nodes independent.
A number of ring controllers are connected together in a closed ring to form the Hub of the star. Node controllers located at the source and destination nodes control message flow into and from the nodes. The ring controllers and node controllers perform many of the same internal functions. However they connect externally to different network media and to either a parallel ring bus in the case of a ring controller or to DMA type of I/O bus of a processor in the case of a node controller. It is advantageous to have single component for both ring controllers and node controllers capable of operating in different modes depending upon the location of the component in the network.
It is therefore an object of the present invention to provide an improved LAN controller that has the ability to connect to a number different interfaces in the network and to be set to operate in a number of different modes.